This invention relates to a slave electronic flash unit for a camera and more particularly to a slave electronic flash unit used together with a camera having a built-in electronic flash and adapted to generate an auxiliary flash in order to compensate inadequacy of the light from the built-in electronic flash.
When flash photography is performed using a camera having a built-in electronic flash (hereinafter simply referred to as a "camera"), if the flash from the built-in electronic flash is the only available light, there may be insufficient light when the distance to an object to be photographed is great. In such a case, in addition to having a built-in electronic flash, a conventional electronic flash unit can be employed as an auxiliary light source in order to compensate the insufficient light. In order to employ a conventional electronic flash unit, a hot shoe having a terminal for transmitting a synchronized signal is mounted on the camera, and then the conventional electronic flash unit is mounted on this shoe. However, if a hot shoe is to be mounted on the camera, the number of the component parts and the number of assembly steps are increased, resulting in high cost of the camera. Also, this is not desirable from the viewpoint of providing a compact camera and achieving an aesthetically pleasing design.
Under these above-mentioned circumstances, a camera such as "RICOH FF70D" (brand name, manufactured by Ricoh Co., Ltd., Japan) is known, in which a slave electronic flash unit for generating an auxiliary flash in addition to that of the built-in flash can be utilized as an auxiliary light source. An adapter for the slave electronic flash is provided as an accessory for this camera. This adapter comprises an L-shaped bracket, a photosensor and an accessory shoe mounted on the L-shaped bracket. The adapter is secured to the camera by the tripod mounting screw hole. During flash photography utilizing this slave electronic flash unit, first, the built-in electronic flash device is actuated by a synchronized signal which is in synchronism with the shutter and generates a flash to illuminate the object. Then when a part of the flash reflected by the object and returned is detected by the photosensor, the slave electronic flash unit mounted on the accessory shoe is actuated to direct the auxiliary flash toward the object.
However, in such a slave electronic flash unit, the photosensor of the adapter is disposed in such a manner as to face forward of the camera so that the sensor can receive the reflected light from the object, and as a result it is adversely affected by light from the surroundings. For example, in the event that a plurality of cameras are used as in an indoor photography contest, there is the drawback that the slave electronic flash unit can accidentally flash at an unexpected time because it responds to a flash generated by a built-in type or mounted-type electronic flash device used in adjacent cameras.